i'm on lamictal. my neurologist didn't say anything about folic acid. my family doc said nothing. my psych (who prescribes it as a mood stabilizer for bipolar disorder) said not to worry about it, it is not really associated with neural tube defects if taken on its own.
i freaked when my OB *did* say i should have been on increased folic acid - but she checked and it's mostly for cleft palate, not NTDs. i was told to take 5mg of folic acid daily, and *keep taking the meds*.
i got pretty pissed off when so many doctors didn't tell me that.. in fact my psych i DID ask specifically, and he said NOT to bother taking extra folic acid. i was so mad!!! but everything is fine. i just had fetal assessment (20w), and amnio, and the baby's neural tube is absolutely FINE. likewise, my sister has a nearly 2 year old, she was on lamictal PLUS other anticonvulsants. in fact in my case, my maternal serum screening (quad screen) came back with LESS than average chance of baby having a neural tube defect. the palate, so far, looks good. my nephew's is totally unaffected.
i'm not sure where you are but you can likely get plain folic acid at a pharmacy. start taking 5mg a day NOW. and then breathe, and make an appointment with your neurologist to discuss your options.
please, don't freak out.. easier said than done, i have literally been there, but i hope i can reassure you with my experience.